The overall goal of this proposal is to prevent the development of autoimmune diabetes by using multivalent MHC class II/peptide chimeras of high valency. The mechanisms and consequences of manipulating the immune system by multivalent MHC II/peptide chimeras will also be investigated. The specific aims are: (1) to determine the protective capacity of soluble, multivalent MHC II/peptide chimeras in autoimmune diabetes as compared to bivalent MHC II/peptide chimera, (2) to study the cellular mechanisms of long-term protection in mice treated with these chimeric molecules , and (3) to study the TR-cell signaling events in mice protected against diabetes by these chimeric molecules. The proposed study will be carried out in a double transgenic mouse model for Type I Diabetes. Satisfactory results will lead to the generation of a human DEF-like molecule (hu- DEF) consisting of the HLA-DR*0401 allele, and the most common diabetogenic peptide in humans, GAD-, and pro-insulin- derived peptides. The therapeutic efficacy of hu-CEF will be evaluated in Tg mice (murine MHcalphabeta class II-/-, human HLA-DR* 0301 and -DR*0401 +/+) after immunization or not with GAD65 peptide, and then adoptively transferred with T-cells from HLA-DR-matched patients with IDDM, or from their at-high risk relatives.